JP2011505663A - Separator on which porous coating layer is formed, method for producing the same, and electrochemical device including the same - Google Patents

Abstract

  The separator of the present invention comprises a porous substrate having a large number of pores, and a porous coating layer coated on at least one surface of the porous substrate and formed of a mixture of a large number of inorganic particles and a binder, The binder includes a binder having a crosslinked structure. The separator having a porous coating layer containing a binder having a cross-linked structure according to the present invention increases the heat resistance, insolubility and impregnation properties of the electrolyte, thereby improving the high temperature cycle performance, discharge characteristics and heat resistance of the electrochemical device. Can be made.

Description

  TECHNICAL FIELD The present invention relates to a separator for an electrochemical element such as a lithium secondary battery and an electrochemical element including the separator, and more specifically, a mixture of inorganic particles and a binder polymer on the surface of a porous substrate. The present invention relates to a separator having a porous coating layer formed thereon and an electrochemical device including the separator.

  Recently, interest in energy storage technology is increasing. As the field of application expands to the energy of mobile phones, camcorders and notebook PCs, and eventually electric vehicles, efforts to research and develop electrochemical devices are becoming more and more concrete. Electrochemical elements are the field that has received the most attention in this respect, and among them, the development of rechargeable secondary batteries is the focus of interest.

  Among secondary batteries currently in use, lithium secondary batteries developed in the early 1990s have been highlighted due to the advantages of higher operating voltage and higher energy density than conventional batteries such as Ni-MH. Yes. However, lithium secondary batteries may explode due to heat generation depending on the usage environment. In particular, polyolefin-based porous substrates commonly used as separators for electrochemical devices exhibit severe thermal shrinkage behavior at temperatures of 100 ° C. or more due to material characteristics and manufacturing process characteristics including stretching. There is a problem of causing a short circuit.

  In order to solve the safety problem of such an electrochemical element, Patent Document 1 and Patent Document 2 disclose a mixture of inorganic particles and a binder polymer on at least one surface of a porous substrate having a large number of pores. A separator with a porous coating layer made of was proposed. In such a separator, the inorganic particles in the porous coating layer formed on the porous substrate serve as a kind of spacer that maintains the physical form of the porous coating layer, thereby allowing the electrochemical element to function. When the substrate is overheated, the porous base material is prevented from being thermally contracted, and even when the porous base material is damaged, the cathode and the anode are prevented from coming into direct contact.

  As described above, the porous coating layer formed on the porous substrate contributes to the improvement of the thermal stability of the electrochemical device, but the development of the separator capable of further improving the heat resistance of the electrochemical device is continued. ing. There is also a need for development of separators that can improve the high temperature cycle performance and discharge characteristics of electrochemical devices.

Korean Patent Publication No. 10-2006-72065 Korean Patent Publication No. 10-2007-231

  Therefore, the problem to be solved by the present invention is to solve the above-mentioned problems and is excellent in thermal stability and not only can suppress a short circuit between the cathode and the anode even when the electrochemical device is overheated, It is an object of the present invention to provide a separator capable of improving the high-temperature cycle performance and discharge characteristics of an electrochemical device by increasing insolubility and impregnation with an electrolytic solution, a manufacturing method thereof, and an electrochemical device including the separator.

  In order to achieve the above object, the separator of the present invention is formed of a porous base material having a large number of pores and a mixture of a large number of inorganic particles and a binder, which is coated on at least one surface of the porous base material. And a porous coating layer, wherein the binder includes a binder having a crosslinked structure.

  In the separator of the present invention, the binder having the crosslinked structure is a binder selected from the group consisting of a polymer having 3 or more reactive groups, a low molecule having 3 or more reactive groups, or a mixture thereof. A binder selected from the group consisting of a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof It may be a binder that is cross-linked to each other by an agent.

  In the separator of the present invention, the binder may be a mixture of a crosslinked binder and a non-crosslinked binder, and the non-crosslinked binder may be polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride). -Co-hexafluoropropylene), polyvinylidenefluoride-trichloroethylene, polymethylmethrylpropylene, polyacrylonitrile (polypropylene), polyacrylonitrile (polypropylene), polyacrylonitrile (polypropylene) (Polyvinylacetate), ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide (polyethylene oxide), cellulose acetate (cellulose acetate), cellulose acetate butyrate (cellulose acetate butyrate) acetic acid propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sulphonate Acetylene-butylene copolymer, acrylonitrile-styrene-butadiene copolymer, unipoly or polymide, and polymide (poly), polynitrile cellulose, pulmonyl cellulose, carboxymethylcellulose, acrylonitrile styrene-butadiene copolymer, Can be used.

  The separator manufacturing method of the present invention comprises (S1) a step of preparing a coating liquid containing a crosslinkable binder component selected from the group consisting of a crosslinkable polymer, a crosslinkable low molecule, and a mixture thereof; A step of producing a coating liquid in which inorganic particles are dispersed by adding inorganic particles to the coating liquid; (S3) forming a coating layer by applying the coating liquid in which the inorganic particles are dispersed to at least one surface of the porous substrate; And (S4) crosslinking the crosslinkable binder component in the coating layer to form a porous coating layer.

  In the separator manufacturing method of the present invention, the crosslinkable binder component is selected from the group consisting of a polymer having three or more reactive groups, a low molecule having three or more reactive groups, or a mixture thereof. Can be used. In addition, the coating liquid may include a crosslinkable binder component and a crosslinking agent selected from the group consisting of a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof. .

  Such a separator can be used for an electrochemical device such as a lithium secondary electron or a supercapacitor device through a cathode and an anode.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments of the invention and serve to explain the principles of the invention in conjunction with the following detailed description of the preferred embodiments. To do.
It is sectional drawing which shows schematically the separator by one Example of this invention. It is sectional drawing which shows schematically the separator by the other Example of this invention.

  Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used in the specification and claims should not be construed in a normal or lexicographic sense, and the inventor will explain his invention in the best possible way. Therefore, in accordance with the principle that the concept of a term can be appropriately defined, it should be interpreted as a meaning and a concept consistent with the technical idea of the present invention. Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. It should be understood that there can be various equivalents and variations that can be substituted for these.

  The separator of the present invention comprises a porous substrate having a large number of pores, and a porous coating layer coated on at least one surface of the porous substrate and formed of a mixture of a large number of inorganic particles and a binder. The binder includes a crosslinked binder. Since the binder constituting the porous coating layer contains a binder having a crosslinked structure, the impregnation ratio with respect to the electrolytic solution is improved, and the discharge characteristics of the electrochemical device due to an increase in ionic conductivity are improved. Further, the solubility of the binder with respect to the electrolytic solution is decreased by the crosslinked structure, thereby improving the stability of the porous coating layer. Furthermore, since the crosslinked binder improves the dimensional stability of the porous coating layer, it contributes to the high temperature performance and stability of the electrochemical device.

In the separator of the present invention, the crosslinked binder may be formed by reacting a polymer having three or more reactive groups, a low molecule having three or more reactive groups, or a mixture thereof, Alternatively, a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof may be cross-linked with a cross-linking agent. Examples of the reactive group include a vinyl group, an epoxy group, a hydroxyl group, an ester group, and a cyanate group that can react by heat or light, and the crosslinking agent has three or more of the above-described reactive groups. A compound can be mentioned. In the following chemical formula 1 and chemical formula 2, a binder component having a reactive group and a crosslinker component are exemplified. A binder having a crosslinked structure is formed by ester reaction between reactive groups, transesterification reaction, urethane reaction, urea reaction, or the like. Binders with low molecular weight cross-links with reactive groups are less flexible and elastic than binders with cross-linked high polymer with reactive groups, but a relatively high degree of cross-linking with smaller amounts. Therefore, it can be used effectively by improving the dimensional stability of the porous coating layer at a high temperature.

  The cross-linked structure is formed by physical or chemical bonding, and examples of the binder having such a cross-linked structure include cross-linked polyethylene oxide, cross-linked polypropylene oxide, cross-linked polymethyl methacrylate, cross-linked polyvinylidene fluoride, and cross-linked polyvinylidene fluoride. Ride-hexafluoropropylene copolymer, cross-linked polyacrylonitrile, cross-linked polysiloxane, cross-linked polyester, cross-linked polyurethane, cross-linked polyurea, cross-linked cellulose acetate or a cross-linked binder of two or more of these can be mentioned, and its weight average molecular weight Is preferably 10,000 g / mol or more.

  In the separator of the present invention, as the binder constituting the porous coating layer, a binder having a non-crosslinked structure may be further mixed in addition to the above-mentioned crosslinked structure binder. Non-crosslinked binders include polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-co-trichloroethylene), poly (vinylidene fluoride-trichloroethylene), and poly (vinylidene fluoride-co-trimethylethylene). polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate) ), Polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpolycyanopropyl Cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose yl cellulose), acrylonitrile-styrene-butadiene copolymer (acrylonitrile-styrene-butadiene copolymer), or polyimide (polyimide) and each alone may be used as a mixture of two or more of these.

In the separator of the present invention, the inorganic particles used for forming the porous coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur in the operating voltage range of the applied electrochemical device (for example, ⁰ to 5 V on the basis of Li / Li ⁺ ). Not limited. In particular, when using inorganic particles having an ion transfer capability, the performance can be improved by increasing the ionic conductivity in the electrochemical element.

  In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolytic solution can be improved by contributing to an increase in the dissociation degree of an electrolyte salt in the liquid electrolyte, for example, a lithium salt.

For the reasons described above, the inorganic particles preferably include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having lithium ion transmission ability, or a mixture thereof. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT). ), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ There are O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, or a mixture thereof.

In particular, BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ Inorganic particles such as (PMN-PT) and hafnia (HfO ₂ ) not only exhibit high dielectric constant characteristics with a dielectric constant of 100 or more, but also when charged or tensioned by applying a certain pressure. Due to the piezoelectricity that generates a potential difference between both surfaces due to the occurrence of the occurrence of internal short circuit between the two electrodes due to external impact, the safety of the electrochemical device can be improved. In addition, when the above-described high dielectric constant inorganic particles and inorganic particles having lithium ion transmission ability are mixedly used, these rising effects can be doubled.

In the present invention, the inorganic particles having lithium ion transfer capability refer to inorganic particles containing lithium element but having a function of moving lithium ions without storing lithium, and having lithium ion transfer capability Since lithium ions can be transmitted and moved by a kind of defect existing inside the particle structure, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the inorganic particles having lithium ion transfer capability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2,0 <y <1,0 <z <3), 14Li 2 O-9Al 2 O ₃ -38TiO ₂ -39P ₂ O _5, such as _(LiAlTiP) x _{O y} series glass (0 <x <4,0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x < 2, 0 <y <3), lithium germanium thiophosphates such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _x Ge _y P _z S _w , 0 <x <4, 0 < y <1, 0 <z <1, 0 <w <5 , Lithium nitride such as _{Li 3 N (Li x N y} , 0 <x <4,0 <y <2), SiS 2 series glasses, such as _{Li 3 PO 4 -Li 2 S-} SiS 2 ( _{Li x Si y S z, 0} <x <3,0 <y <2,0 <z <4), P 2 S 5 series glass such as _{LiI-Li 2 S-P 2} S 5 (Li x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof.

  In the separator of the present invention, the size of the inorganic particles in the porous coating layer is not limited, but it should be in the range of 0.01 to 10 μm as much as possible in order to form a coating layer with a uniform thickness and appropriate porosity. Is desirable. When the thickness is less than 0.01 μm, the dispersibility is lowered and it is not easy to adjust the physical properties of the separator. When the thickness exceeds 10 μm, the thickness of the porous coating layer is increased and the mechanical properties can be lowered. The excessive pore size increases the probability of an internal short circuit during battery charging / discharging.

  The composition ratio between the inorganic particles of the porous coating layer coated on the separator according to the present invention and the binder having a crosslinked structure is, for example, preferably in the range of 50:50 to 99: 1, and more preferably in the range of 60:40 to 95: 5. It is. The thickness of the porous coating layer composed of the inorganic particles and the binder is not particularly limited, but is preferably in the range of 0.01 to 20 μm. The pore size and porosity are not particularly limited, but the pore size is preferably in the range of 0.01 to 10 μm, and the porosity is preferably in the range of 5 to 90%.

  The separator of the present invention may further contain other additives in addition to the aforementioned inorganic particles and polymer as components of the porous coating layer.

  In the separator of the present invention, any porous substrate that is usually used in electrochemical devices can be used as the porous substrate on which the porous coating layer is formed.

  Referring to FIG. 1, a separator 10 of the present invention uses a porous polyolefin-based membrane 1 a as a porous substrate, and has a porous structure composed of a binder 5 having a structure in which one side or both sides are crosslinked with inorganic particles 3. A coating layer may be formed. Polyolefin porous membranes are, for example, polyethylene polymers such as high density polyethylene, linear low density polyethylene, low density polyethylene, and ultrahigh molecular weight polyethylene, polypropylene polymers such as polypropylene, polybutylene, and polypentene, either singly or in combination. A membrane formed of a polymer can be given.

  In addition, as shown in FIG. 2, the separator 20 of the present invention uses a nonwoven fabric 1b as a porous substrate, and a porous coating layer comprising a binder 5 having a structure in which one side or both sides are crosslinked with inorganic particles 3 Can be formed. Examples of the non-woven fabric include, in addition to the above-described polyolefin-based non-woven fabric, for example, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polymide, polymide, polymide, polymide, polymide, polymide, and polymide. , Polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylenesulfene (polyphenylenesulfurene), polyphenylenesulfide (polyphenylenesulfide), polyphenylene oxide (polyphenylenesulfide), polyphenylene sulfide (polyphenylenesulfide) fidro), or alone respectively or polyethylene naphthalene (polyethylenenaphthalene), mention may be made of nonwoven fabric formed by these mixed polymer. The structure of the nonwoven fabric is preferably a spunbond type nonwoven fabric or a melt-blown nonwoven fabric composed of long fibers.

  The thickness of the porous substrate is not particularly limited, but is preferably 5 to 50 μm, and the size and porosity of the pores existing in the porous substrate are not particularly limited, but are 0.01 to 50 μm and 10 to 95%, respectively. It is desirable to be.

  Although the desirable manufacturing method of the separator by which the porous coating layer was coated by this invention is illustrated below, it is not limited to this.

  First, a coating liquid containing a crosslinkable binder component selected from the group consisting of a crosslinkable polymer, a crosslinkable low molecule, and a mixture thereof is prepared (Step S1).

  As described above, as the crosslinkable binder component, a polymer having three or more reactive groups, a low molecule having three or more reactive groups, or a mixture thereof can be used. Moreover, the coating liquid containing a crosslinkable binder component comprises a crosslinkable binder component which is a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof, and a crosslinking agent. Can be included. If necessary, a crosslinking initiator such as a thermal initiator or a photoinitiator and a reaction catalyst can be further added to the coating solution.

  When only a crosslinkable polymer is used as the crosslinkable binder component, a coating solution is prepared by dissolving in a suitable solvent. When a crosslinkable low molecule is contained as the crosslinkable binder component, the crosslinkable polymer can be dissolved in the crosslinkable low molecule, and thus there is a case where a solvent may not be used.

  As the solvent, those having a solubility index similar to that of the crosslinkable polymer or crosslinkable low molecule to be used and having a low boiling point are desirable. This is because mixing can be made uniform and the solvent can be easily removed thereafter. Non-limiting examples of solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N-methyl-). 2-pyrrolidone (NMP), cyclohexane, water or mixtures thereof.

  Next, inorganic particles are added to the prepared coating liquid to produce a coating liquid in which the inorganic particles are dispersed (step S2).

  It is desirable to crush the inorganic particles after adding the inorganic particles to the coating liquid. At this time, the crushing time is appropriately 1 to 20 hours, and the particle size of the crushed inorganic particles is preferably 0.01 to 10 μm as described above. As a crushing method, a usual method can be used, and a ball mill method is particularly desirable.

  Thereafter, the coating liquid in which the inorganic particles are dispersed is applied to at least one surface of the porous substrate to form a coating layer (step S3).

  As a method of coating the porous substrate with the coating liquid in which the inorganic particles are dispersed, a conventional coating method known in the art can be used, for example, dip coating, die coating, roll Various methods such as a (roll) coating, a comma coating, or a mixed method thereof may be used. Further, the porous coating layer can be selectively formed only on both surfaces or one surface of the porous substrate.

  Next, the crosslinkable binder component in the coating layer is crosslinked to form a porous coating layer (step S4).

  For crosslinking of the crosslinkable binder component, a curing method commonly used in the art can be used. For example, when the coating layer can be thermally cured, it can be cured batchwise or continuously by treatment at a temperature between room temperature and 200 ° C. in an oven or a heated chamber. Moreover, when a coating layer can be hardened | cured by photoreaction, what is necessary is just to cure by irradiating light at appropriate temperature. When a condensate or a side reaction product is generated during the curing reaction, it is desirable to perform the curing under a reduced pressure, and the pressure is adapted to 0.01 to 500 torr. A rapid pressure reduction condition of 0.01 torr or less is difficult to be realized as a mass production condition, and a condensate or a side reaction product is not easily removed under a pressure condition of 500 torr or more.

  Needless to say, when a solvent is added to the coating solution, an additional drying process of the coating layer is required. Drying conditions can be batch or continuous using an oven or heated chamber in a temperature range that takes into account the vapor pressure of the solvent used.

  The separator of the present invention thus produced can be used as a separator for electrochemical devices. That is, the separator of the present invention is usefully used as a separator interposed between the cathode and the anode.

  Electrochemical elements include all elements that react electrochemically, and, by way of example, all kinds of capacitors such as primary, secondary batteries, fuel cells, solar cells, or supercapacitor elements. and so on. In particular, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferable.

  The electrochemical device can be manufactured by a conventional method known in the art. For example, after assembling the separator between the cathode and the anode through the separator, It can be manufactured by injection. When applying the separator of the present invention, an ordinary polyolefin-based porous membrane can be used together as necessary.

  The electrode applied together with the separator of the present invention is not particularly limited, and can be manufactured in a form in which an electrode active material is bound to an electrode current collector according to a usual method known in the art. Among the electrode active materials, as a non-limiting example of the cathode active material, a conventional cathode active material conventionally used as a cathode of an electrochemical device can be used, particularly lithium manganese oxide, lithium cobalt oxide, It is desirable to use lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these. As a non-limiting example of the anode active material, a conventional anode active material conventionally used as an anode of an electrochemical element can be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activation Lithium adsorbents such as activated carbon, graphite or other carbons are desirable. Non-limiting examples of cathode current collectors include foils made from aluminum, nickel or combinations thereof, and non-limiting examples of anode current collectors include copper, gold, nickel or There are foils manufactured from copper alloys or combinations thereof.

The electrolyte that can be used in the present invention is a salt having a structure such as A ⁺ B ⁻ , and A ⁺ is an ion composed of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ , or a combination thereof. B ⁻ is PF ₆ ⁻ , BF ₄ ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) _{2 ^{-, C (CF 2 sO 2}} ) 3 - anions or salts, propylene carbonate containing ions a combination thereof, such as (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate ( DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydro Examples include, but are not limited to, those dissolved or dissociated in organic solvents consisting of orchid, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or mixtures thereof. It is not done.

  The electrolyte can be injected at an appropriate stage in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, the present invention can be applied before battery assembly or at the final stage of battery assembly.

  As a process of applying the separator of the present invention to a battery, in addition to a general process of winding, there can be a lamination and stacking process of a separator and an electrode and a folding process. In particular, when the separator of the present invention is applied to the laminating process among the above processes, the effect of improving the thermal stability of the electrochemical device becomes significant. This is because the thermal contraction of the separation membrane is more severe in the battery manufactured by the stacking and folding process than in the battery manufactured by the general winding process. In addition, when the separator of the present invention is applied to the laminating process, it can be easily assembled at a higher temperature due to the excellent thermal stability and adhesive strength characteristics of the crosslinked binder.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified in many forms, and the scope of the present invention should not be construed to be limited to the embodiments described later. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

Example 1
1-1. Production of Separator A crosslinkable binder (TA10, 2% by weight) represented by the following chemical formula 3 and AIBN (0.04% wt / wt) as a crosslinking initiator in acetone at about 30 ° C. for about 1 It was dissolved for hours. To this solution, an alumina powder having an average particle size of about 1 μm was added and dispersed at a concentration of 20% by weight of the total solid content. Thereafter, this mixed solution was coated on a polyethylene porous substrate (porosity 35%) having a thickness of about 20 μm by using a dip coating method, and was simultaneously cured and dried in a drying oven at 90 ° C. for about 10 minutes. The thickness of the finally formed coating layer was adjusted to be about 2 μm. As a result of measurement with a porosity measuring device (porosimeter), the size and porosity of the pores in the porous coating layer formed on the polyethylene porous substrate were 0.4 μm and 40%, respectively.

1-2. Production of Lithium Secondary Battery N-methyl-2-pyrrolidone as a solvent with LiCoO ₂ 94% by weight as a cathode active material, carbon black 3% by weight as a conductive material, and PVdF 3% by weight as a binder (NMP) was added to produce a cathode mixture slurry. The cathode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 μm, which was a cathode current collector, and dried to produce a cathode.

  Anode powder slurry was prepared by adding carbon powder as an anode active material, PVdF as a binder, and carbon black as a conductive material to 96 wt%, 3 wt%, and 1 wt%, respectively, to NMP as a solvent. The anode mixture slurry was applied to a 10 μm thick copper (Cu) thin film serving as an anode current collector and dried to produce an anode.

The cathode, anode, and separator manufactured by the above-described method are assembled in a stacking manner, and ethylene carbonate / propylene carbonate / diethyl carbonate (EC) in which 1M lithium hexafluorophosphate (LiPF ₆ ) is dissolved in the assembled battery. / PC / DEC = 30: 20: 50 wt%) based electrolyte solution was injected to manufacture a lithium secondary battery.

Example 2
A separator and a lithium secondary battery were manufactured in the same manner as in Example 1 except that a polyethylene terephthalate nonwoven fabric having a thickness of about 20 μm was used as the porous substrate. The pore size of the porous coating layer of the manufactured separator was 0.6 μm or less, and the porosity was at the 55% level.

Comparative Example 1
A separator and a lithium secondary battery were manufactured in the same manner as in Example 1 except that PVdF-HFP was used at 2% by weight instead of the crosslinkable binder and the crosslinking initiator. The pore size of the porous coating layer of the manufactured separator was 0.5 μm or less, and the porosity was at a level of 42%.

Comparative Example 2
A separator and a lithium secondary battery were produced in the same manner as in Example 2 except that PVdF-HFP was used at 2% by weight instead of the crosslinkable binder and crosslinking initiator used in Example 2. . The pore size of the porous coating layer of the manufactured separator was 0.8 μm or less, and the porosity was at the 58% level.

  The high-temperature performance and high-temperature safety of the batteries manufactured according to the above-described examples and comparative examples were evaluated as follows.

Cycle performance at 60 ° C. Each battery according to the example and comparative example was subjected to 1C / 1C charge / discharge cycle experiment at a high temperature of 60 ° C., and the percentage value obtained by dividing the capacity measured after 100, 200, and 300 cycles by the initial capacity. Are shown in Table 1.

In the battery of the example using the separator having the porous coating layer containing the binder having a crosslinked structure according to the present invention, the capacity decrease is larger as the number of charge / discharge cycles is larger than the battery of the comparative example as the control group. Results were significantly reduced. This is because the use of a binder having a structure crosslinked at a high temperature of 60 ° C. increases the thermal stability of the porous coating layer of the separator, thereby maintaining a stable interface with the electrode. It shows that the high-temperature performance has greatly increased.

Discharge characteristics (C-rate)
The batteries of the examples and comparative examples were cycled at discharge rates of 0.2C, 0.5C, 1C, and 2C, respectively, at room temperature, and these discharge capacities were calculated as a percentage of the 0.2C capacity for each C-rate characteristic. Table 2 below.

  The battery of the example using the separator provided with the porous coating layer containing the binder having a crosslinked structure according to the present invention has a very small decrease in the discharge capacity due to the increase of the discharge speed as compared with the battery of the comparative example as the control group. I understand that. This is considered to be because the porous coating layer containing a binder having a crosslinked structure increases the impregnation ratio with respect to the electrolytic solution, thereby improving the ionic conductivity of the battery.

The batteries of the hot box experimental examples and comparative examples were stored at a high temperature of 150 ° C. and 160 ° C. for 1 hour and 2 hours, respectively, and the state of the batteries is shown in Table 3 below.

As shown in Table 3, when the batteries of Comparative Examples 1 and 2 were stored at a temperature of 160 ° C. for 2 hours, an explosion phenomenon of the batteries appeared. In comparison, the batteries of Examples 1 and 2 were safe when stored at 160 ° C. for 2 hours. This means that the cross-linked binder greatly increases the thermal stability of the porous coating layer, preventing internal short circuit between the cathode and anode even when the battery is stored for long periods at high temperatures. To do.

  A separator having a porous coating layer containing a binder having a crosslinked structure according to the present invention is insoluble in an electrolyte and has improved dimensional stability at high temperatures, so that a cathode and an anode can be used even when an electrochemical device is overheated. The short circuit can be suppressed, and the high-temperature cycle characteristics of the electrochemical element are improved. Moreover, since the impregnation property with respect to the electrolyte solution of a separator increases, the discharge characteristic by ionic conductivity improvement improves.

DESCRIPTION OF SYMBOLS 1a ... Polyolefin-type porous membrane 1b ... Nonwoven fabric 3 ... Inorganic substance particle 5 ... Binder of the bridge | crosslinked structure 10 ... Separator 20 ... Separator

Claims (14)

A porous substrate having a large number of pores;
It is coated on at least one surface of the porous substrate, and comprises a porous coating layer formed of a mixture of a large number of inorganic particles and a binder,
The separator includes a binder having a crosslinked structure.   The binder having the crosslinked structure is crosslinked by a reaction between binders selected from the group consisting of a polymer having three or more reactive groups, a low molecule having three or more reactive groups, or a mixture thereof. The separator according to claim 1, wherein the separator is a bonded binder.   The cross-linked binder is a polymer selected from the group consisting of a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof. The separator according to claim 1, wherein the separator is a crosslinked binder.   The separator according to claim 1, wherein the binder is a mixture of the crosslinked structure binder and the non-crosslinked structure binder.   The non-crosslinked binder may be polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride-co-trichloroethylene, polyvinylethylene fluoride-co-trichloroethylene). polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate) , Polyethylene oxide (polyethylene oxide), cellulose acetate (cellulose acetate), cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpulylpropylene (cyanoethylpropylene) Ethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose 1 cellulose), acrylonitrile-styrene-butadiene copolymer, and one or a mixture of two or more selected from the group consisting of polyimide and polyimide 4. The separator according to 4.   The separator according to claim 1, wherein the inorganic particles have a size of 0.01 to 10 µm.   The separator according to claim 1, wherein a weight ratio of the inorganic particles and the crosslinked binder is 50:50 to 99: 1.   The separator according to claim 1, wherein the pore size of the porous coating layer is 0.01 to 10 µm, and the porosity of the pores of the porous coating layer is 5 to 95%. .   The separator according to claim 1, wherein the porous substrate is a polyolefin-based porous film.   The porous substrate is made of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyether, ether, polyether, ether, polyether, ether polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene And wherein the selected from the group consisting of Polyethylenenaphthalene) is any type of polymer or nonwoven fabric made of a mixture of two or more, separator according to claim 1. (S1) providing a coating liquid containing a crosslinkable binder component selected from the group consisting of a crosslinkable polymer, a crosslinkable low molecule, and a mixture thereof;
(S2) adding inorganic particles to the coating liquid to produce a coating liquid in which the inorganic particles are dispersed;
(S3) applying a coating liquid in which the inorganic particles are dispersed to at least one surface of a porous substrate to form a coating layer; and (S4) cross-linking the crosslinkable binder component in the coating layer to make the coating layer porous. A method for producing a separator, comprising the step of forming a conductive coating layer.   The crosslinkable binder component is any one selected from the group consisting of a polymer having 3 or more reactive groups, a low molecule having 3 or more reactive groups, or a mixture thereof. The separator manufacturing method according to claim 11, wherein   The coating liquid contains a crosslinkable binder component and a crosslinking agent selected from the group consisting of a polymer having two or more reactive groups, a low molecule having two or more reactive groups, or a mixture thereof. The manufacturing method of the separator of Claim 11 characterized by these. An electrochemical element,
A cathode, an anode, and a separator interposed between the cathode and the anode,
The said separator is a separator as described in any one of Claims 1-10, The electrochemical element characterized by the above-mentioned.

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